Chiralpak IC Research Articles

Total syntheses of borolithochromes H1, H2, I1, and I2.

Total syntheses of borolithochromes H1, H2, I1, and I2, the red pigments isolated from fossils of Jurassic putative red alga Solenopora jurassica, have been achieved. The naphthoquinone possessing a chiral sec-butyl side chain has been synthesized from (S)-2-methylbutanol. The Diels-Alder reaction of the chiral naphthoquinone and the previously reported diene was followed by one pot S-methylation/intramolecular Corey-Chaykovsky reaction/epoxide rearrangement to provide the benzo[gh]tetraphene skeleton. Complexation of the resulting ligand with trimethyl borate and the following O-demethylation furnished a 1:1 mixture of borolithochromes I1 and I2, which were separated by HPLC using CHIRALPAK IC® to afford optically pure borolithochromes I1 (6) and I2 (7). On the other hand, borolithochromes H1 and H2 were not separated by HPLC in our laboratory. Fortunately, the mixture of the methyl ethers of borolithochromes H1 and H2 were separated and O-demethylation with magnesium iodide furnished optically pure borolithochromes H1 (4) and H2 (5).

Enantioselective polar-organic mode high-performance liquid chromatographic separation of lifitegrast on immobilized polysaccharide stationary phase and its application to pH-dependent chiral interconversion studies.

(S)-Lifitegrast (LFT) is the novel integrin antagonist, approved by the Food and drug administration, to treat signs and symptoms of dry eye disease. Synthesis of racemic LFT, preparative and analytical enantiomer separation, and chiral interconversion studies are lacking in the literature. Hence, in our study, synthesis of LFT racemate, chiral preparative purification procedure of enantiomer, and comprehensive analytical advancements are focused on rapid enantioselective separation and pH-dependent chiral interconversion studies. The synthesis of LFT racemate employed 2-amino-3-(3-(methylsulfonyl)phenyl)propanoic acid hydrochloride and 2-(benzofuran-6-carbonyl)-5,7-dichloro-1,2,3,4-tetrahydroisoquinoline-6-carbonyl chloride as starting materials. (R)-LFT was isolated from the racemate by preparative chiral HPLC and characterized using Q-TOF, FT-IR, NMR spectroscopy, and chiral HPLC. The purity of (R)-LFT was determined to have an enantiomeric excess of 99.12%. A precise, accurate, rapid HPLC-DAD enantioselective analytical method has been developed on Chiralpak IC [tris(3,5-dichloro phenyl carbamate) immobilized on cellulose] using water and methanol as mobile phase. The chiral interconversion study reveals 0.22% and 0.21% of interconversion of (S)-LFT into (R)-LFT at 80°C in pH7.4 and 9.5 buffers, respectively, on the 24th day. An alternative route to enantioselective synthesis of LFT enantiomers by chromatographic separation is proposed. The validated enantioselective HPLC method will help to test the regular quality control samples.

Two Pairs of New Bisabolane-Type Sesquiterpenoids from Aspergillus sydowii.

Two pairs of new bisabolane-type sesquiterpenoids, (+)-aspersydowin A (7S) [(+)-1], (-)-aspersydowin A (7R) [(-)-1], (+)-aspersydowin B (7S,11S) [(+)-2], (-)-aspersydowin B (7R,11R) [(-)-2], along with six known compounds (1-8) were isolated from the fungus Aspergillus sydowii. Compounds 1 and 2 are enantiomers resolved by the Chiralpak IC, using a hexane- propan-2-ol mobile phase. The structure of 1 and 2 with absolute configuration were assigned tentatively by 1D (1 H, 13 C, and DEPT) & 2D (HSQC, 1 H-1 H COSY, HMBC, and NOESY) NMR data analyses and ECD calculations. Compounds 1-8 were screened for the biological activities in vitro. The results showed that compounds 3, 4 and 8 exhibited immunosuppressive activities with IC50 values of 10.9, 17.6 and 13.4 μM, respectively.

Comparative studies of immobilized polysaccharide derivatives chiral stationary phases for enantioseparation of furanocoumarins and dihydroflavones and discussion on chiral recognition mechanism.

Enantiomeric separation of furanocoumarins and dihydroflavones compounds were systematically studied in the normal-phase mode using four different polysaccharide-type chiral stationary phases, namely, Chiralpak IA, Chiralpak IC, Chiralpak IG, and Chiralpak IK-3 by high-performance liquid chromatography. The effect of alcohol modifiers and alcohol content on enantiomeric separation was evaluated for the separation of furanocoumarins and dihydroflavones. All the eight compounds have achieved baseline separation with the resolutions ranging between 1.52 and 23.11. For a better insight into the enantiorecognition mechanisms, thermodynamic analysis was carried out. The mechanisms of chiral recognition have been discussed. Among four chiral columns, Chiralpak IG exhibited the most universal and the best enantioseparation ability toward furanocoumarins and dihydroflavones when used n-hexane-isopropanol and n-hexane-ethanol as mobile phase, respectively. The steric hindrance, hydrogen bonding, and π-π interaction played major roles in chiral recognition on Chiralpak IG. By comparing four chiral columns, this work systematically analyzed the separation methods of furanocoumarins and dihydroflavones for the first time and reported some active chiral ingredients of traditional Chinese medicine that have never been separated, which provided a further insight into the enantioseparation of furanocoumarins and dihydroflavones on chiral stationary phases.

Enantiomeric Separation and Degradation of Benoxacor Enantiomers in Horticultural Soil by Normal-Phase and Reversed-Phase High Performance Liquid Chromatography.

The separation of benoxacor enantiomers on six commercial chiral columns was investigated by high-performance liquid chromatography (HPLC) under normal-phase and reversed-phase conditions. The mobile phases included hexane/ethanol, hexane/isopropanol, acetonitrile/water, and methanol/water. The effects of the chiral stationary phases (CSPs), temperature, and mobile phase composition and ratio on the separation of benoxacor enantiomers were examined. Under normal-phase conditions, the two benoxacor enantiomers were completely separated on Chiralpak AD, Chiralpak IC, Lux Cellulose-1, and Lux Cellulose-3 columns and partially separated on a Lux Cellulose-2 column. Under reversed-phase conditions, benoxacor enantiomers were completely separated on a Lux Cellulose-3 column and partially separated on Chiralpak IC and Lux Cellulose-1 columns. Normal-phase HPLC performed better than reversed-phase HPLC for the separation of benoxacor enantiomers. As the column temperature increased from 10 °C to 4 °C, the enthalpy (ΔH) and entropy (ΔS) results indicated that the resolution was strongly affected by the temperature and that the lowest temperature did not always produce the best resolution. An optimized separation method on the Lux Cellulose-3 column was used to investigate the stability of benoxacor enantiomers in solvents and the degradation of benoxacor enantiomers in three types of horticultural soil. Benoxacor enantiomers were stable, and degradation or racemization were not observed in methanol, ethanol, isopropanol, acetonitrile, hexane, or water (pH = 4.0, 7.0, and 9.0). In three horticultural soils, the degradation rate of S-benoxacor was faster than that of R-benoxacor, resulting in soil enrichment with R-benoxacor. The results of this study will help to improve the risk assessment of enantiomer levels of benoxacor in the environment.

An on-line heart-cutting two-dimensional liquid chromatography method for intracellular 2-hydroxyglutarate enantiomers.

D-2-Hydroxyglutarate (D-2-HG) is an oncometabolite that induces cancer cell survival and growth. D-2-HG is produced by mutations in isocitrate dehydrogenases 1 and 2. L-2-HG has different roles than the D-form, and chiral discrimination is important for elucidating the exact roles of the 2-HG enantiomers. In this study, an analytical method for 2-HG enantiomers was developed using on-line heart-cutting two-dimensional liquid chromatography (2D-LC) with fluorescence detection. Fluorescence derivatization of 2-HG with 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was performed using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, a hydrophilic condensing reagent, at 70 °C for 30 min. The first dimension on the octadecylsilyl column was aimed at separating NBD-PZ-2-HG from other compounds obtained via derivatization or from biological fluids. The NBD-PZ-2-HG peak was fractionated into a sample loop and automatically injected into the second dimension. In the second dimension, a CHIRALPAK IC column separated NBD-PZ-D- and L-2-HG with a resolution of 2.14. The limits of quantification were 0.25 pmol per injection for NBD-PZ-D-2-HG and-L-2-HG. The precision values were below 6.58%, and the accuracies were 88.2-92.8%. The intracellular concentrations of D-2-HG and L-2-HG in the cancer cells were 13.5 ± 0.4 and 9.9 ± 0.3 pmol per 1.0 × 106 cells, respectively. The developed method will be useful for elucidating the role of 2-HG enantiomers in cancer cells.

Chiral separation of conazole pesticides using supercritical fluid chromatography

ABSTRACT Supercritical fluid chromatographic methods for enantiomer separation of six conazole-type antifungal pesticides (bromuconazole, cyproconazole, prothioconazole, tebuconazole, ipconazole, triticonazole) are presented in this work. Screening tests on six different chiral analytical columns (Chiralpak IA, Chiralpak IB, Chiralpak IC, Chiralpak AS, Chiracel OJ and Kromasil Cellucoat) were carried out using methanol as organic modifier. Cellulose-based stationary phases were found to be better for separation of each tested conazole, than the amylose-based columns. The influence of the most commonly used co-solvents (methanol, ethanol and 2-propanol) on the separation was also studied on selected columns. Suitable analytical methods were found for enantiomer separations for all studied conazoles; moreover, the methods are good starting points to semi-preparative separation. The importance of sample solvent selection in the semi-preparative separation of triticonazole isomers was proved. Acetonitrile as sample solvent resulted in a narrow, nice peaks compared to those obtained with methanol or dichloromethane. Twenty milligrams of each enantiomer of triticonazole was collected for ecotoxicity testing using the analytical size column.

Enantioseparation and quantitative analysis of three alkaloids in Rhizoma Corydalis by chiral LC-MS/MS

A chiral liquid chromatography-mass spectrometry (LC-MS/MS) approach was developed and verified for the first time in order to quantify the three alkaloids, namely tetrahydropalmatine (THP), tetrahydroberberine (THB) and tetrahydrocoptisine (THC) in Rhizoma Corydalis. Solid-phase extraction was used to prepare sample solution. Enantiomeric separation was obtained on a Chiralpak IC column using acetonitrile-water-ammonia (90:10: 0.1, v/v/v) as mobile phase. The detection was carried out in multiple reaction monitoring (MRM) mode with positive electrospray ionization source. Transitions of m/z 356.0→192.0, m/z 340.0→176.0 and m/z 324.1→176.0 were monitored for THP, THB and THC respectively. All calibration curves showed good linearity (r2 ≥0.9994) within the test ranges. The lower limit of quantification (LLOQ) was 1.0 ng mL−1 and 1.5 ng mL−1 for (+)- and (−)-THP, 1.0 ng mL−1 and 3.0 ng mL−1 for (+)- and (−)-THB, 1.5 ng mL−1and 1.8 ng mL−1 for (+)- and (−)-THC, respectively. The precision, repeatability, and stability tests all meet the requirements. The average recoveries of the analytes ranged from 98.9 % to 101.3 %. Ultimately, the established method was successfully applied to the quantitative analysis of these alkaloid enantiomers extracted from Rhizoma Corydalis of different habitats.

Enantioseparation and determination of oxypeucedanin and its application to a stereoselective analysis in Angelica Dahuricae Radix and pharmacokinetic study of rats

In this study, a new enantioseparation method was established for the quantitative analysis of the oxypeucedanin enantiomers by using cellulose tris(3,5-dichlorophenyl carbamate) stationary phase column Chiralpak IC. For this method, enantiomeric separation of oxypeucedanin was achieved with the mobile phase consisting of acetonitrile-water (60:40, v/v) at a flow rate of 0.5 mL/min by changing the type and proportion of mobile phase. And the quantitative determination of racemic oxypeucedanin in Angelica Dahuricae Radix (in vitro) and rat plasma (in vivo) were performed on above-mentioned condition by High PerformanceLiquid Chromatography combined with diode arrangement detector (HPLC-DAD) and mass spectrometry (HPLC-MS/MS). The precision, repeatability, stability, recovery were within the acceptance criteria. And the method was validated in the concentration range of 1-400 μg/mL for the two enantiomers in vitro and 0.2–600 ng/mL in vivo. After validation, the established method was successfully applied to the stereoselective analysis of racemic oxypeucedanin in Angelica dahurica from different regions and the stereoselective pharmacokinetic investigation in rat. Results showed that the (+)-oxypeucedanin was at a relative high level in Angelica dahuricae Radix and (−)-oxypeucedanin performed a higher plasma concentration, which demonstrated the difference of oxypeucedanin enantiomers both in vitro and in vivo.

Quality by design approach for enantioseparation of terbutaline and its sulfate conjugate metabolite for bioanalytical application using supercritical fluid chromatography

Terbutaline is mainly metabolized by sulfoconjugation stereoselectively, favoring its (S)-(+) enantiomer. Reported chiral separations of Terbutaline enantiomers were achieved by various chromatographic methods. However, the simultaneous enantioseparation of Terbutaline and the monosulfate conjugate metabolites was never reported. This study aims at shedding light on the influential factors and interactions leading to successful enantioseparation of Terbutaline and its monosulfate conjugate pairs by Supercritical Fluid Chromatography (SFC) for the first time within a Quality by Design framework using Design of Experiments. The effect of molarity of mobile phase additive, mobile phase flow rate, column temperature and back pressure were evaluated. Compared to previous reports, the response surface interestingly revealed the favorability of high temperature and high flow rate up to 2.25 ml/min for resolution of the two pairs of enantiomers on polysaccharide chiral stationary phase CHIRALPAK IC. In addition, a switch in the elution order of Terbutaline and the sulfate conjugate peak pairs was observed upon elimination of the mobile phase additive where the sulfate conjugate underwent intra-molecular ionic interactions and the change in elution order was only due to TER behavior. The multifactorial interactions would not have been detected with the common one-factor-at-a-time approach during method development, demonstrating the superiority and importance of the Analytical Quality by Design frame in enantioseparation.

Stability-indicating HPLC method development and validation of rivaroxaban impurities and identification of forced degradation products using LC-MS/MS.

The current aim of this study is to develop a simple, sensitive, and robust analytical method that can separate the Rivaroxaban and its related impurities by using HPLC. This new method can separate enantiomers and all the process-related impurities of rivaroxaban. This method can also be used to determine the assay of rivaroxaban in drug substances and drug products. This new method was developed using a Chiralpak IC (250 × 4.6mm, 5μm) column at 27°C with a gradient program of 25.0min at a flow rate of 0.8mL/min. Mobile phase A consisted of acetonitrile, ethanol, and n-butyl amine in the ratio of 95:5:0.5 (v/v/v), respectively. Mobile phase B consisted of a mixture of Milli-Q water, methanol, and n-butyl amine in the ratio of 50:50:0.5 (v/v/v), respectively. The detector wavelength was 254 nm. Rivaroxaban was subjected to the forced degradation conditions (stress conditions) of hydrolysis, base, acid, thermal, photolysis, and oxidation. The degradation products were well separated from rivaroxaban peak and enantiomer peak, and its potential impurities prove the stability-indicating power of the method. The proposed new stability-indicating method was validated with respect to specificity, precision, accuracy, limit of quantification, limit of detection, linearity robustness, and roundness per International Conference on Harmonization guidelines. The %RSD (relative standard deviation) for six sample preparations for rivaroxaban and impurities less than 10% and the recovery is between 90 and 110%. The current method can be used in quality control labs for analysis of commercial products.

Development of a novel HPLC-ESI-MS/MS method to analyze the stereoselective pharmacokinetics and tissue distribution of isoconazole enantiomers in rats.

Isoconazole with an asymmetrical carbon is a broad-spectrum antimicrobial imidazole, but there is still lack of relevant report about the potential enantioselectivity in biological samples. The object of this research was to develop and validate a sensitive and effective high performance liquid chromatography-electrospray ionization coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method for stereoselective separation and determination of isoconazole enantiomers in Sprague-Dawley (SD) rat plasma and tissues. The greater enantioseparation of isoconazole enantiomers was obtained on a Chiralpak IC column with a mobile phase consisted of acetonitrile-10 mM aqueous ammonium acetate (90:10, v/v) under the reversed-phase mode. Subsequently, the studied compounds and internal standard (IS) were detected on a multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The experimental and theoretical Electronic Circular Dichroism (ECD) spectra were employed to confirm the absolute configuration of isoconazole enantiomers. Eventually, after full method validation, the newly developed method was successfully applied to the study of enantioselectivity in plasma and tissues in SD rats. Results illustrated that the enantioselective differences in plasma were observed for the evidence that the concentrations of S-(-)-isoconazole were always higher than R-(+)-isomer. In terms of tissue distribution, liver, kidney, lung, spleen, and small intestine were the mainly distributed tissues and then followed by heart and muscle. This is the first study to reveal the stereoselective behavior of isoconazole enantiomers in vivo, which also provides reliable and valuable reference for further elucidating the enantioselective metabolisms of isoconazole enantiomers.

Application of Polysaccharide-Based Chiral High-Performance Liquid Chromatography Columns for the Separation of Regio-, E/Z-, and Enantio-Isomeric Mixtures of Allylic Compounds.

Daicel Chiralpak IA, IB, and IC, which are the polysaccharide-based chiral stationary phase (CSP) columns for high-performance liquid chromatography (HPLC), were applied in the separation of the non-enantiomeric isomeric mixtures obtained by the various allylation reactions and were highly effective in separating the regio- and (E)/(Z)-isomers in the allylation products. Due to the close structural similarity of the isomeric allylic compounds in the reaction mixtures, separations of the isomers are laborious and could not be accomplished by the conventional methods such as silica gel column chromatography, silica gel HPLC, preparative GPC, distillation, and so forth. This study has shown potential advantages of using the polysaccharide-based CSP columns in the separation of not only enantiomeric but also non-enantiomeric isomeric mixtures.

Development and Validation of Teneligliptin Stereoisomers by HPLC Using Cellulose Based Immobilized Polysaccharide Chiral Stationary Phase

Background: There is no single chiral method for the quantitation of teneligliptin stereoisomers by high performance liquid chromatography (HPLC). Hence, there is a need for the quantification of teneligliptin (TNGP) and its stereoisomers. Objective: The main aim of the research work is to develop a novel simple, selective, precise and accurate HPLC method for the separation of TNGP and its stereoisomers. Methods: Different screening trials were executed by changing the mobile phase compositions to normal phase and polar mode and also by utilizing the different immobilized polysaccharide chiral columns like CHIRALPAK IA, IC, ID, IE, IF and IG. All the stereoisomers were eluted with high resolution, on CHIRALPAK IC-3 (4.6×250 mm), 3 μm chiral stationary phase (CSP) with a flow rate of 0.7 mL/min. The chromatographic system was processed with isocratic mode comprising ethanol: acetonitrile: ethanolamine in the proportion of 90:10:0.1% v/v/v with a column oven temperature of 15°C and detection wavelength of 250 nm. Results: The limit of detection (LOD) and limit of quantification (LOQ) values of TNGP(API), R,S-isomer, S,R-isomer and R,R-isomer were found to be 0.036/0.11, 0.029/0.09, 0.038/0.011 and 0.020/0.06 μg/mL, respectively. The method was found to be precise, accurate and linear (R2 > 0.999). Conclusion: The developed method was successfully applied for the quantification of bulk drug without any interference with the extraneous components. Hence, the method can be utilized successfully in the pharmaceutical organizations for the separation and quantification of TNGP isomers.

Enantioseparation and Determination of Sulcoanzole Enantiomers in Rat Plasma and Tissues by Chiral HPLC-ESI-MS/MS Method Coupled with SPE Procedure and Its Application to the Studies on Stereoselective Pharmacokinetics and Tissue Distribution

In our research, a novel reverse phase mode high performance liquid chromatography-electrospray ionization coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method for the rapid and sensitive enantioselective analysis of sulconazole in rat plasma and tissues was developed and validated. A newly developed solid phase extraction (SPE) procedure using C18 cartridge was selected for the extraction of sulconazole and internal standard (IS, ornidazole) from plasma and tissues. The excellent enantioseparation of sulconazole enantiomers was achieved on a Chiralpak IC column by using acetonitrile/5 mM aqueous ammonium acetate (90:10, v/v) as a mobile phase, and the detection of the targeted compounds and IS was performed on a multiple reaction monitoring (MRM) mode with positive electrospray ionization source. Using the measured Electronic Circular Dichroism (ECD) spectrum combined with the calculated ECD spectrum, the absolute configuration of sulconazole enantiomers was confirmed and was used to identification of the elution peak order. The S-(+)-sulconazole was first eluted. After comprehensive validation following the FDA-guideline, the method was linear over concentration ranges of 1.00-500.0 ng/mL (R2>0.991) for each enantiomer. The mean recoveries of S-(+)- and R-(-)-sulconazole at three spiked levels ranged from 88.7-102.5%, the intra- and inter-day relative standard deviation (RSD) were limited within 10.3%. The established method was successfully applied to the study on stereoselective pharmacokinetics and tissue distribution in Sprague-Dawley rats after transdermal administration of rac-sulconazole spray. It should be noted that this is the first report regarding the stereospecific study of sulconazole enantiomers in vivo.

Polysaccharide-based chiral stationary phases as efficient tools for diastereo- and enantioseparation of natural and synthetic Cinchona alkaloid analogs

In this study, we present results obtained on the diastereo- and enantioseparation of some basic natural and synthetic Cinchona alkaloid analogs by applying liquid chromatographic (LC) and subcritical fluid chromatographic (SFC) modalities on amylose and cellulose tris-(phenylcarbamate)-based stationary phases using n-hexane/alcohol/DEA or CO2/alcohol/DEA mobile phase systems. Seven chiral stationary phases in their immobilized form were employed to explore their stereoselectivity for a series of closely related group of analytes. The most important characteristics of LC and SFC systems were evaluated through the variation of the applied chromatographic conditions (e.g., the nature and content of the alcohol modifier, the concentration of additives, temperature). The columns Chiralpak IC and IG turned out to be the best in both LC and SFC modalities. Temperature-dependence study indicated enthalpy-controlled separation in most cases; however, separation controlled by entropy was also registered.

Enantioseparation of lysine derivatives on amylose tris (3, 5-dimethylphenylcarbamate) as chiral stationary phase with high separation factor

Enantioseparation of lysine derivatives by chiral high-performance liquid chromatography (HPLC) was accomplished using two chiral stationary phases (CSPs, Chiralpak IA and Chiralpak IC) based on polysaccharides under normal phase (NP) conditions. All analytes were completely separated. The impacts of polar modifiers, analyte structure and column temperature on chiral separation were discussed. Moreover, the relationship between structure and retention was investigated. The van't Hoff equation was employed to evaluate the thermodynamic parameters of the chiral separation process. The data suggest that the chiral separation process was enthalpy-driven. Surprisingly, two uncommon phenomena were observed: (1) high separation factors on Chiralpak IA and (2) different binding mechanisms with CSP and the two enantiomers.

Chiral Separation and Determination of Etoxazole Enantiomers in Vegetables by Normal-Phase and Reverse-Phase High Performance Liquid Chromatography.

The chiral separation of etoxazole enantiomers on Lux Cellulose-1, Lux Cellulose-3, Chiralpak IC, and Chiralpak AD chiral columns was carefully investigated by normal-phase high performance liquid chromatography and reverse-phase high performance liquid chromatography (HPLC). Hexane/isopropanol, hexane/n-butanol, methanol/water, and acetonitrile/water were used as mobile phase at a flow rate of 0.8 mL/min. The effects of chiral stationary phase, mobile phase component, mobile phase ratio, and temperature on etoxazole separation were also studied. Etoxazole enantiomers were baseline separated on Lux Cellulose-1, Chiralpak IC, and Chiralpak AD chiral columns, and partially separated on Lux Cellulose-3 chiral column under normal-phase HPLC. However, the complete separation on Lux Cellulose-1, Chiralpak IC, and partial separation on Chiralpak AD were obtained under reverse-phase HPLC. Normal-phase HPLC presented better resolution for etoxazole enantiomers than reverse-phase HPLC. Thermodynamic parameters, including ΔH and ΔS, were also calculated based on column temperature changes from 10 °C to 40 °C, and the maximum resolutions (Rs) were not always acquired at the lowest temperature. Furthermore, the optimized method was successfully applied to determine etoxazole enantiomers in cucumber, cabbage, tomato, and soil. The results of chiral separation efficiency of etoxazole enantiomers under normal-phase and reverse-phase HPLC were compared, and contribute to the comprehensive environmental risk assessment of etoxazole at the enantiomer level.

Enantioseparation and Determination of Penconazole in Rat Plasma by Chiral LC-MS/MS: Application to a Stereoselective Toxicokinetic Study.

In this study, a specific and sensitive method of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was developed for the determination of penconazole enantiomers in rat plasma. The enantioseparation was achieved on a Chiralpak IC column by using acetonitrile/water (80:20, v/v) as the mobile phase. Penconazole enantiomers and internal standard l-lansoprazole (IS) were detected in multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The method was validated over the concentration range of 2.5–250.0 ng mL−1 for penconazole enantiomers. Good linearity was obtained for both enantiomers with correlation coefficients (R) greater than 0.995. The relative error was well within the admissible range of −1.1–3.2%, and relative standard deviation was less than 6.0%. After validation, the established method was successfully applied to a stereoselective toxicokinetic study in female and male rats after oral administration of 50 mg kg−1 racemic penconazole. This is the first experiment regarding the stereospecific toxicokinetic study of penconazole and the bioanalytical approach for its quantitation in vivo.

Simultaneous enantioselective determination of omeprazole, rabeprazole, lansoprazole, and pantoprazole enantiomers in human plasma by chiral liquid chromatography-tandem mass spectrometry.

Proton pump inhibitors, including omeprazole, rabeprazole, lansoprazole, and pantoprazole, achieved simultaneous enantioselective determination in the human plasma by chiral liquid chromatography-tandem mass spectrometry. The four corresponding stable isotope-labeled proton pump inhibitors were adopted as the internal standards. Each enantiomer and the internal standards were extracted with acetonitrile containing 0.1% ammonia, then separated with a Chiralpak IC column (5 µm, 4.6mm × 150mm) within 10 min. The mobile phase was composed of acetonitrile-ammonium acetate (10mM) containing 0.2% acetic acid (50:50, v/v). To quantify all enantiomers, an API 4000 tandem mass spectrometer was used, and multiple reaction monitoring transitions were performed on m/z 360.1→242.1, 384.1→200.1, 370.1→252.1, and 346.1→198.1, respectively. No significant matrix effect was observed for all analytes. The calibration curve for all enantiomers were linear from 1.25 to 2500ng/mL. The precisions for intra- and inter-run were<14.2%, and the accuracy fell in the interval of -5.3 to 8.1%. Stability of samples was confirmed under the storage and processing conditions. The developed method was also suitable for separation and determination of ilaprazole enantiomers. The validated method combining the equilibrium dialysis method was applied to the protein binding ratio studies of four pairs proton pump inhibitor enantiomers in human plasma.